Silvio Berlusconi, besieged as never before by sex and drug allegations, went on the offensive today, dismissing claims against him as "made-up stories" and hinting the mafia may have framed him in reprisal for recent police successes.

"No one today can rule out with certainty that certain things that are happening are not the fruits of an underworld vendetta," he told a meeting of his Freedom People (PdL) party's leadership. "In what other country in the world would the head of the government have to defend himself against a barrage of made-up stories?"

The prime minister earlier caused renewed controversy with alleged remarks to the lower house speaker, Gianfranco Fini, at a parade for Italian armed forces day. Lip readers reported him saying "She is of age" and, while gesticulating excitedly, adding that the woman he was alluding to had a clean police record.

According to the weekly L'Espresso, the office of the prosecutor in charge of an inquiry into the alleged aiding and abetting of prostitution by Berlusconi associates has been burgled. The break-in took place in late August, the magazine said, two days after the office of the judge overseeing the inquiry was also burgled.

The most recent of the stories that Berlusconi claims are untrue was told to prosecutors on Sicily by a 27-year-old ex-prostitute, Nadia Macri, who says she twice supplied him with sexual services. The second time, according to newly leaked extracts from her deposition, was in a swimming pool at Berlusconi's home at Arcore near Milan, with a girl who was "young. Very young: 17-18 years old".

Just as damaging is Macri's claim that, when she flew – along with 25 or 30 other young women – to his Sardinian villa, "There was also grass to smoke in the rooms. The girls said the [marijuana] was transported by Berlusconi's jet."

Berlusconi has been at the centre of a series of scandals in recent years, including claims by a prostitute, Patrizia D'Addario, that she had sex with him in 2008. Berlusconi has denied paying for sex. There was also controversy over his friendship with a teenage model, Noemi Letizia.

Neither of the most recent allegations, however, would seem to make the prime minister liable to criminal charges, even if they were true. The age of consent in Italy is 14. Prostitution is not illegal, though profiting from it is. And there is nothing in what is so far known of Macri's statement to indicate Berlusconi himself supplied the drugs allegedly used at the holiday estate where he has hosted Tony Blair, Vladimir Putin and other world leaders.

The biggest legal threat arose from another young woman, Karima el- Mahroug, a then 17-year-old belly dancer who is reported to have told prosecutors in Milan that she attended three parties at Arcore, but denies any sexual entanglement with the prime minister.

Mahroug was detained by police in May on suspicion of stealing €3,000 (£2,620), but after a call from the prime minister's office, she was handed over to a Berlusconi acquaintance – his former dental hygienist, who was this year elected to the Lombardy regional parliament.

Yesterday, the chief prosecutor of Milan decided there were no grounds for bringing a case against the prime minister for abusing his position, which is an offence in Italy. The ruling appeared to clear the way for today's upbeat counter-blast in which the media mogul told his lieutenants: "We're not going to take steps back, but five leaps forward."

That was a reference to the five points in his government's programme for the rest of the legislature. Awkwardly for Berlusconi, one is to provide improved support for the family.

On Monday, he is due to address a conference on the family in Milan where the archbishop, Cardinal Dionigi Tettamanzi, declared that the "Italy of today is sick, as Milan was in the time of plagueand Saint Charles Borromeo" (Lombardy's 16th-century patron whose feast day falls today)". But the cardinal's words seemed to have little impact on some of the many devout Catholics among Berlusconi's supporters. "Let's leave out the moralising," said Maurizio Lupi, the PdL's deputy lower house speaker. "In politics, support for a government is assessed on the basis of the actions it takes." Berlusconi has firmly backed the Vatican's line on a range of issues, notably IVF and stem cell research.

At the weekend, Fini's followers will take a decision that could settle the fate of the government. In July, they renounced the PdL whip and have since made plans to form a party of their own.

But they remain in the government, and Berlusconi today sent a veiled warning that, if they tried to leave, he would resign. "We are ready to pick up the gauntlet and go straight to the polls," he said.

"He knows Fini doesn't want an election," said James Walston, professor of international relations at the American University of Rome. "Fini's people cannot afford to upset a conservative electorate that would think he was being radical and irresponsible [deserting the government]. In any case, they are not organised yet."

Walston said that the trade unions, employers' federation and most of the other parties were all keen to avoid elections. "Berlusconi has it relatively easy. What people outside Italy don't understand is that he is still extraordinarily strong."

His most famously loyal supporter, the presenter Emilio Fede, denies supplying girls to him. "Since he lost his mother, his life has become much sadder," Fede said. "If one evening a week he wants to enjoy himself, I don't see any wrong in it."

Dangerous liaisons

July 2008 Berlusconi pushes through a law granting immunity from prosecution for the four highest office holders in Italy, including himself

May 2009 Berlusconi's second wife, Veronica Lario says she wants a divorce, after he attends Noemi Letizia's 18th birthday party

June 2009 Recordings of Berlusconi and escort girl Patrizia D'Addario emerge. In the same month, photos appear in El País newspaper showing topless women and naked men at his villa in Sardinia. The paper also accuses him of using state aircraft to fly guests to and from the island

October 2009 Italy's constitutional court overturns law that granted Berlusconi immunity while in office

October 2010 Karima Keyek, 17, claims Berlusconi paid her €7,000 (£6,100) and gave her jewellery when she attended two of his parties. It is also claimed he ordered police to release her from custody after she was accused of stealing